1. Field of the Invention
The present invention relates to a process for the production of polyesterpolycarbonate.
2. Description of the Prior Art
It is known that a copolymer of polycarbonate and polyester, i.e., polyesterpolycarbonate, has been developed for the purpose of improving heat-resistance, etc. of polycarbonate. Various methods have been proposed for the production of polyesterpolycarbonate, including (1) a solution method and (2) an interfacial polymerization method. In accordance with the solution method (1), bisphenol A and terephthalic acid chloride are reacted in pyridine and phosgene is introduced into the reaction mixture to perform polycondensation (see Japanese Patent Application Laid-Open No. 128992/1977). Since, however, this method uses pyridine, it is not commercially satisfactory in view of various problems, such as its recovery and unpleasant odor.
The interfacial method (2) has been developed as an improved process for the solution method (1), including (2-a) a three-stage polycondensation method in which an aqueous alkaline solution of dihydric phenols and an organic solvent solution of terephthalic acid chloride and isophthalic acid chloride are reacted to prepare polyester oligomers, phosgene is then reacted with the polyester oligomer, and furthermore, dihydric phenol is reacted therewith (see Japanese Patent Application Laid-Open Nos. 25427/1980 and 38824/1980) and (2-b) a method in which phosgene is added to polyester oligomer (see Japanese Patent Application Laid-Open Nos. 822/1981 and 823/1981). These methods (2-a) and (2-b), however, suffer from various disadvantages. For example, in the method (2-a), it is necessary to perform phosgenation of polyester oligomers, and the method (2-b) fails to produce polyesterpolycarbonate having a uniform composition (polycarbonate homopolymers are liable to be formed). The polycarbonate unit contained in polyesterpolycarbonate as produced by the above-described methods is one or a mixture composed mainly of one polycarbonate unit, and cannot be controlled appropriately or optionally. Furthermore, problems arise in combining the methods to conventional polycarbonate production steps.